Check a monitor now (and deliver a signed webhook if it changed)

Runs one check immediately with the same billing as a scheduled check (baseline: feed 10, sitemap flat 10, techstack 30; no change: 2 / 5; change: full price, sitemap 10 + 1 per changed URL; delivering a sitemap change needs at least 11 credits (10 base + 1 per URL); a check that finds no change costs 2; carried-over URLs 1 each, no second base fee). If something changed and the monitor has a webhookUrl, a real signed monitor.change is POSTed (one attempt). Bound by the minimum monitor interval, the same on every plan (429 + Retry-After), and 30 runs/hour per account. Works for monitors with or without schedule:true. Failed checks are not charged.